Name of part

I had my fuel pump replaced, and the mechanic did a poor job reattaching a big plastic cover beneath the SUV. It began to hang, the drag. I need a new one now. No one seems to know what it is. It's attached behind the bumper and is about 3 feet by 18 in. Does anyone know what's it is called. ? I was thinking. "Splash guard", but I am not sure. Thanks in advance for your help!